Activated carbon sorbent including nitrogen and methods of using the same

ABSTRACT

The present invention relates to activated carbon sorbents including nitrogen. In various embodiments, the present invention provides an activated carbon sorbent including a halogen- or halide-promoted activated carbon, the activated carbon sorbent particles including nitrogen in a surface layer of the sorbent particles. In various embodiments, the present invention provides a method of reducing the pollutant content in a pollutant-containing gas using the activated carbon sorbent. In various embodiments, the activated carbon sorbent can remove mercury from a mercury-containing gas that includes sulfur(VI) such as SO3 more efficiently than other sorbents.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No. 15/589,359, filed May 8, 2017, which is a continuation of U.S. patent application Ser. No. 14/195,360, filed Mar. 3, 2014, now issued as U.S. Pat. No. 9,669,355, which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/773,549, filed Mar. 6, 2013, the disclosures of which are incorporated herein in their entireties by reference.

BACKGROUND OF THE INVENTION

Mercury (Hg) emissions have become a health and environmental concern because of their toxicity and ability to bioaccumulate. The U.S. Environmental Protection Agency (EPA) has issued regulations for the control of mercury emissions from waste-to-energy, cement production, and coal-fired power plants. Mercury in flue gas from industrial sources (e.g., power plants) can be captured by sorbents such as activated carbon, which can then be removed by particulate separation devices. The amount of standard sorbents (e.g., activated carbon) needed to serve the market is large. Standard sorbents are not always effective and become more expensive as larger amounts are used.

Inhibition of mercury capture from gas streams by active carbon sorbents can occur when sulfur(VI) (e.g. SO₃, H₂SO₄) is present in the gas stream, with increasing inhibition at higher concentrations. Mercury capture above sulfur(VI) concentrations of 3 ppm by mole is limited. Many utilities desire to operate SO₃ injection systems at a minimum of about 5-6 ppm to improve ash collectability. However, a sulfur(VI) concentration of about 6 ppm can diminish elemental mercury capture by about 25%-50% or more. With this reduction, it becomes difficult, if not impossible, to economically achieve desired mercury levels. The scientific understanding of why a severe inhibition of mercury sorption exists when sulfur(VI) concentrations increase by such a small amount is limited.

SUMMARY OF THE INVENTION

In various embodiments, the present invention provides an activated carbon sorbent. The activated sorbent includes a halogen- or halide-promoted carbon. The activated carbon includes activated carbon sorbent particles including nitrogen. The concentration of nitrogen in a surface layer of the sorbent particles is at least one of 1) higher than the concentration of nitrogen in a core of the sorbent particles and 2) higher than the concentration of nitrogen in the carbon material from which the sorbent particles are derived.

In various embodiments, the present invention provides a method of making an activated carbon sorbent. The method includes contacting a carbonaceous material and a nitrogenous material, to provide an unpromoted carbon sorbent comprising nitrogen. The method also includes promoting at least a portion of the unpromoted sorbent by contacting the portion of the unpromoted sorbent with a promoter to form an activated carbon sorbent comprising activated carbon sorbent particles comprising nitrogen, wherein the concentration of nitrogen in the sorbent particles is higher than the concentration of nitrogen in the carbonaceous material.

In various embodiments, the present invention provides an activated carbon sorbent for use in mercury removal from a mercury-containing gas. The activated carbon sorbent includes a halogen- or halide-promoted inorganic activated carbon particles including nitrogen in a surface layer of the sorbent particles. The nitrogen atoms are at sufficient concentration in the surface layer of the activated carbon sorbent particles to at least one of a) decrease neutralization by HSO₃ ¹⁻ or SO₃ ²⁻ of carbocations in the activated carbon sorbent, as compared to a corresponding activated carbon sorbent comprising less or substantially no nitrogen in a corresponding particle surface layer under substantially similar conditions, and b) at least partially block carbocations in the activated carbon from forming ionic bonds with HSO₃ ¹⁻ or SO₃ ²⁻, as compared to a corresponding activated carbon sorbent including less or substantially no nitrogen in a corresponding particle surface layer under substantially similar conditions.

In various embodiments, the present invention provides a method of reducing the pollutant content in a pollutant-containing gas. The method includes obtaining or providing an activated carbon sorbent including activated carbon sorbent particles including nitrogen in a surface layer of the sorbent particles. The method includes contacting a pollutant-containing gas with the activated carbon sorbent. The contacting forms a pollutant-sorbent composition. The method also includes separating at least some of the pollutant-sorbent composition from the pollutant-containing gas. The separating gives a separated gas.

In various embodiments, the present invention provides a method for reducing the mercury content of a mercury-containing gas. The method includes obtaining or providing a carbon precursor. The carbon precursor includes nitrogen. The method includes obtaining or providing a substrate material. The method includes contacting the carbon precursor and the substrate material. The contacting provides an inorganic matrix-supported sorbent starting material. The method includes heating the inorganic matrix-supported sorbent starting material. The heating provides an unpromoted sorbent. The method includes promoting at least a portion of the unpromoted sorbent by contacting (e.g., chemically reacting) the portion of the unpromoted sorbent with a promoter to form a promoted inorganic matrix-supported activated carbon sorbent. The activated carbon sorbent includes activated carbon sorbent particles including nitrogen in a surface layer of the sorbent particles. The method includes contacting the mercury-containing gas with the activated carbon sorbent. The contacting forms a mercury-sorbent composition. The method also includes separating at least some of the mercury-sorbent composition from the mercury-containing gas. The separating gives a separated gas. The concentration of sulfur(VI) in the mercury-containing gas is about 3-1000 ppm by mole. A first quantity of the activated carbon sorbent forms a mercury-sorbent composition at a first mercury adsorption rate. The first adsorption rate is higher than a mercury absorption rate of the first quantity of a corresponding activated carbon sorbent including at least one of a) less or substantially no nitrogen in a corresponding particle surface layer, b) less or substantially no halide- or halogen-promotion, and c) less or substantially no inorganic matrix support.

In various embodiments, the present invention provides a method of making an activated carbon sorbent. The method includes obtaining or providing an unpromoted carbon sorbent including nitrogen. The method includes promoting at least a portion of the unpromoted sorbent by contacting (e.g., chemically reacting) the portion of the unpromoted sorbent with a promoter to form an activated carbon sorbent including activated carbon sorbent particles including nitrogen in a surface layer of the sorbent particles.

Various embodiments of the present invention provide certain advantages over other activated carbon sorbents and methods of using the same, at least some of which are unexpected. In some embodiments, the activated carbon sorbent can separate a material (e.g., a pollutant) from a gas that includes that material more efficiently than other methods. In various embodiments, mercury removal efficiencies of the activated carbon exceed or match that of conventional methods with added benefits such as reduced costs. The method and materials of various embodiments of the present invention can operate more efficiently than other methods of mercury removal. In some embodiments, the method and materials of various embodiments can remove a given amount of mercury for a smaller amount of financial expenditure, as compared to other methods. For example, the method and materials of various embodiments can remove a larger amount of mercury for a given mass of carbon, as compared to other methods of removing mercury, including as compared to other methods of removing mercury that include a carbon sorbent.

For example, in some embodiments, a given mass of the nitrogen-containing activated carbon sorbent can absorb mercury from a mercury-containing gas stream including sulfur(VI) (e.g., SO₃, H₂SO₄, or the like), such as greater than about 3 ppm sulfur(VI), such as about 3-200 ppm sulfur (VI), 3-1000 ppm sulfur(VI), or about 3-10 ppm sulfur(VI), at a higher rate than the same mass of a corresponding activated carbon sorbent including less or no nitrogen, such as a lower concentration of nitrogen or no nitrogen in a corresponding particle surface layer. In some embodiments, carbocations in the activated carbon sorbent are neutralized less by ions derived from SO₃, such as SO₃ ²⁻ or HSO₃ ¹⁻, than other activated carbon sorbents, such as other activated carbon sorbents including less or substantially no nitrogen in a corresponding particle surface layer. In some embodiments, carbocations in the activated carbon sorbent are at least partially blocked from ions derived from SO₃, such as SO₃ ²⁻ or HSO₃ ¹⁻, more than in other activated carbon sorbents, such as in other activated carbon sorbents including less or substantially no nitrogen in a corresponding particle surface layer.

In some embodiments, the sorbent can be regenerated and reused, reducing disposal of spent sorbents and decreasing the cost of mercury removal. In some embodiments, preparation or promotion of the activated carbon sorbent can advantageously occur on site. On site preparation and promotion can have advantages including, for example: reduction or elimination of equipment costs and operating costs of a separate preparation facility or location, reduction or elimination of transportation costs, fresher and more reactive sorbent, reduction of handling, on-site tailoring of composition (such as when changing fuels or reducing loads).

In some embodiments, counter to traditional teachings that inorganic components can hinder sorption of pollutants on activated carbon, an inorganic matrix support in the sorbent can enhance the sorption of pollutant in the activated carbon, such as on a proximate and oxidatively reactive carbon graphene layer. In various embodiments, an inorganic matrix support can stabilize the development of cationic sites on the proximate graphene carbon structures which can oxidize pollutants such as mercury. In embodiments that include an inorganic matrix-supported nanocomposite that is promoted via a hydrogen halide compound obtained from degradation or reaction of the corresponding ammonium halide, another advantageous role for the inorganic portion can be in providing a binding site for the ammonia that is released from either the decomposition or reaction of the ammonium salt. The bound ammonia can form a complex with basic character that can react with SO₂ or SO₃ in the pollutant-containing gas and can prevent their interference with the sorption of pollutants such as mercury in or near active sites on the activated carbon.

Clays are usually difficult to filter or separate from an aqueous medium. In some embodiments that include clay as an inorganic matrix support, the clay is advantageously stabilized to dispersion in an aqueous medium, and can be easily separated from an aqueous medium by filtration.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to certain embodiments of the disclosed subject matter. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.

Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of “about 0.1% to about 5%” or “about 0.1% to 5%” should be interpreted to include not just about 0.1% to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement “about X to Y” has the same meaning as “about X to about Y,” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise.

In this document, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

In the methods of manufacturing described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed step of doing X and a claimed step of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

Definitions

The term “about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

The term “substantially” as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

The term “number-average molecular weight” as used herein refers to the ordinary arithmetic mean of the molecular weight of individual molecules in a sample. It is defined as the total weight of all molecules in a sample divided by the total number of molecules in the sample. Experimentally, the number average molecular weight (M_(n)) is determined by analyzing a sample divided into molecular weight fractions of species i having n_(i) molecules of molecular weight M_(i) through the formula M_(n)=ΣM_(i)n_(i)/Σn_(i). The number average molecular weight can be measured by a variety of well-known methods including gel permeation chromatography, spectroscopic end group analysis and osmometry.

The term “weight-average molecular weight” as used herein refers (M_(w)), which is equal to ΣM_(i) ²n_(i)/ΣM_(i)n_(i), where n_(i) is the number of molecules of molecular weight M_(i). In various examples, the weight average molecular weight can be determined using light scattering, small angle neutron scattering, X-ray scattering, and sedimentation velocity.

The term “solvent” as used herein refers to a liquid that can dissolve a solid, liquid, or gas. Nonlimiting examples of solvents are silicones, organic compounds, water, alcohols, ionic liquids, and supercritical fluids.

The term “air” as used herein refers to a mixture of gases with a composition approximately identical to the native composition of gases taken from the atmosphere, generally at ground level. In some examples, air is taken from the ambient surroundings. Air has a composition that includes approximately 78% nitrogen, 21% oxygen, 1% argon, and 0.04% carbon dioxide, as well as small amounts of other gases.

The term “room temperature” as used herein refers to a temperature of about 15° C. to 28° C.

As used herein, “mineral” refers to a naturally occurring solid chemical substance formed through biogeochemical processes, having, for example, characteristic chemical composition, highly ordered atomic structure, and specific physical properties.

Description

In various embodiments, the present invention provides an activated carbon sorbent and associated method for reduction of mercury content for use in combustion systems that have inherently high levels of sulfur(VI) (e.g. as SO₃, or related compounds that can be derived therefrom such as H₂SO₄ or other sulfates) in the flue gas and for use in plants that use SO₃ injection for ash conditioning for improved ash collection. The method can obtain high mercury capture rates in a high sulfur(VI)-content flue gas by, in some examples, overcoming the kinetic and equilibrium effects that can inhibit mercury capture in high SO₃ or high-sulfate (e.g. high sulfur(VI)) systems. The activated carbon sorbent includes activated carbon sorbent particles. The concentration of nitrogen in a surface layer of the sorbent particles can be higher than the concentration of nitrogen in a core of the sorbent particles. In some examples, the activated carbon sorbent can be promoted.

In various embodiments, the activated carbon sorbent and associated method can be effective for removal of elemental mercury vapor in an air or flue gas stream at moderate temperatures (e.g., about 25-330° C., or about 50-500° C.). In some examples, the activated carbon is not impregnated with sulfur or metal halides, which can be unstable at higher temperatures.

In some embodiments, the removal process does not involve adsorption of the elemental mercury like that occurring at low temperatures, but can involve the catalyzed reaction of mercury with an oxidant to form an organomercury compound that includes the mercury bound to the activated carbon surface, wherein the mercury can be released via, e.g., reaction with acid, to provide a mercury (II) species with low vapor pressures such as mercury sulfate, mercury bromide, or mercury chloride. The ionic mercury(II) form can be an oxide or salt of an optional acid used in the process (such as sulfate from sulfuric acid), which can have lower volatility. The activated carbon can exhibit a high rate of oxidative catalytic activity due to, for example, numerous active catalytic sites and, at the same time, possess a large surface area for generation of the organomercury compound and thus rapidly generate the converted mercury(II) salt.

Activated Carbon Sorbent Including Nitrogen.

In various embodiments, the present invention provides an activated carbon sorbent. The activated carbon sorbent can include halogen- or halide-promoted activated carbon particles; in other embodiments, the activated carbon sorbent is not promoted. In some examples, the activated carbon can have an inorganic matrix-support.

The activated carbon sorbent can include activated carbon sorbent particles. The concentration of nitrogen in a surface layer of the sorbent particles can be at least one of 1) higher than the concentration of nitrogen in a core of the sorbent particles and 2) higher than the concentration of nitrogen in the activated carbon material from which the activated carbon sorbent particle was derived. The surface layer of each particle can independently be continuous (e.g., unbroken, with minimal or no gaps) or non-continuous. The surface layer can be at the outer surface of the particle. The surface layer of each particle can independently have any suitable thickness. The surface layer can have a variable thickness, or can have a substantially consistent thickness. In some embodiments, the surface layer can have a thickness of about 0.000,001% to about 99.99% of the radius of the particle, 0.001% to 99%, 0.001% to about 50%, 1% to about 50%, 0.1% to 25%, or about 25% to 50% of the radius of the particle. If the particle is non-spherical the radius can be estimated as about one-half of the largest dimension of the particle.

In some embodiments, each activated carbon particle can independently include about 1.001 times higher nitrogen concentration in the surface layer than in the core or less, or about 1.01, 1.1, 1.2, 1.4, 1.6, 1.8, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 50, 100, or about 1000 times higher nitrogen concentration in the surface layer than in the core. In some embodiments, the concentration of nitrogen in the surface layer can be about 0.000,001 wt % or less, or about 0.001 wt %, 0.01 wt %, 0.1 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 10 wt %, 15 wt %, 20 wt %, 30 wt %, 40 wt %, 50 wt %, 60 wt %, 70 wt %, 80 wt %, or about 90 wt % or more nitrogen. In some examples, the concentration of nitrogen in the surface layer can be about 0.001 wt %-99 wt % nitrogen, 5 wt %-80 wt %, or about 5-60 wt %. In various embodiments, the concentration of nitrogen in the core can be about 0 wt %, 0.000,001 wt %, or about 0.001 wt %, 0.01 wt %, 0.1 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 10 wt %, 15 wt %, 20 wt %, 50 wt %, or 90 wt % or more. In some examples, the concentration of nitrogen in the core can be about 0.001 wt %-99 wt % nitrogen, 0.1 wt %-20 wt % or about 1 wt %-6 wt %.

The activated carbon sorbent can be in any suitable form. For example, the activated carbon can be granular, or fine particles. The activated carbon can have any suitable shape, such as spherical or irregular. The activated carbon can have an average diameter of about 0.1 nm or less, or about 1 nm, 10 nm, 100 nm, 1 μm, 10 μm, 100 μm, 1 mm, or about 10 mm or more. In some examples, the activated carbon has a diameter of about 0.01 μm or less, or about 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 1000 μm or more. In some examples, the diameter of the particle is about 0.1-1000 μm, or 1-100 μm, or about 1-30 μm. If a particle is non-spherical, the diameter can be estimated as the longest dimension of the particle. The absorption capacity of the activated carbon sorbent including mercury can be about 0.000,1 mg mercury per gram of sorbent or less, or about 0.001 mg/g, 0.01, 0.1, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 150, 200, 300, 400, 500, 750, or about 1 g mercury per gram of sorbent or more.

In some embodiments, at least some of the carbon in the activated carbon is in the graphene form of carbon. The graphene form of carbon can, in some embodiments, include higher concentrations of locations suitable as active sites. In some examples, certain parts of graphene carbon can have the highest concentrations of locations suitable as active sites: in some examples at the edges, in some examples in non-edge locations. Such locations suitable as active sites may be activated via treatment with halide or halogen, as described herein. In various embodiments, the carbon in the activated carbon sorbent can be at least about 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 10 wt %, 20 wt %, 30 wt %, 40 wt %, 50 wt %, 60 wt %, 70 wt %/o, 80 wt %, 90 wt %, 95 wt %, 96 wt %, 97 wt %, 98 wt %, 99 wt %, 99.9 wt %, 99.99 wt %, or more than about 99.999 wt % graphene form of carbon.

In some embodiments, the nitrogen is substantially homogenously distributed throughout the activated carbon particles. In some embodiments, the nitrogen is substantially homogenously distributed in the core of the activated carbon sorbent particles; in other embodiments, the nitrogen can have any suitable distribution in the core. In some embodiments, the nitrogen is substantially homogenously distributed in the surface layer of the activated carbon sorbent particles. In some embodiments, the nitrogen in the surface layer is not homogeneously distributed; e.g., the nitrogen can have a gradient with the highest concentration at the outside of the surface layer and a lower concentration at an inside of the surface layer.

The nitrogen can be in any suitable form within the activated carbon. In some examples, the nitrogen can be a nitrogen atom bound to one or more hydrogen atoms or one or more other atoms that are, for example, carbon-containing groups that are part of the activated carbon framework (e.g. the activated carbon backbone or appendages thereof), or to an organic group. In some examples, for example, the nitrogen can be neutral or can bear a positive charge (e.g. ammonium) or a negative charge. The nitrogen can have any suitable oxidation state, for example zero or one. The nitrogen can be bound to 4, 3, 2, 1, or zero hydrogen atoms. The nitrogen can be bound to one or more activated carbon frameworks at zero, 1, 2, 3, or 4 locations. In some embodiments, the nitrogen can include one or two double bonds or one triple bond to the carbon framework of the activated carbon or to other functional groups, such that the nitrogen is bound to 1, 2, or 3 carbon atoms.

The nitrogen in the activated carbon can be derived from any nitrogen containing compound, such as a nitrogen-containing organic or inorganic compound, such as by pyrolysis or carbonization. In some examples, the nitrogen is derived from or part of any nitrogen-containing heterocycle, or from any other nitrogen-containing compound. For example, the nitrogen can be derived from indole, quinoxaline, carbazole, isoquinoline, piperazine, quinolone, quinoxaline, diazabicyclooctane, polyacrylonitrile, polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymer, vinylpyrrolidone-acrylic acid copolymer, vinylpyrrolidone-maleic acid copolymer, polyethylenimine, an amino acid (e.g., alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, or valine), analine, nitrobenzene, hydroxylamine, urea, hydrazine, sulfamic acid, nitriles, carbamates, isocyanates, urethanes, or a combination thereof. In some examples, the nitrogen in the activated carbon can be derived from or part of a nitrogen-containing inorganic compound, such as ammonia, ammonium bromide, ammonium chloride, nitric acid, nitrous acid, nitrogen dioxide, compounds including NO₃, compounds including NO₂, and the like.

In various embodiments, the nitrogen-containing activated carbon sorbent can absorb pollutants such as mercury at a higher rate in a given concentration of sulfur(VI) than other sorbents. In some examples, a first quantity of the activated carbon sorbent forms a mercury-sorbent composition at a first mercury adsorption rate in a gas composition including mercury wherein the concentration of sulfur(VI) in the gas composition is about 3-2000 ppm by mole, where the first adsorption rate is higher than a mercury absorption rate of the first quantity of a corresponding activated carbon sorbent including at least one of a) less (e.g., lower concentration) or substantially no nitrogen in a corresponding particle surface layer, b) less or substantially no halide- or halogen-promotion, and c) less or substantially no inorganic matrix support.

The mechanism of operation of the activated carbon sorbent is not intended to be limited to any particular theory of operation as advanced herein. In some embodiments, the nitrogen in the surface layer at least partially decreases neutralization by SO₃ (or ions or other materials derived from SO₃ such as HSO₃ ¹⁻ or SO₃ ²⁻) of carbocations in the activated carbon sorbent, as compared to a corresponding activated carbon sorbent including less or substantially no nitrogen in a corresponding particle surface layer under substantially similar conditions. In some examples, the nitrogen in the surface layer at least partially blocks carbocations in the activated carbon from forming ionic bonds with SO₃ (or ions or other materials derived from SO₃ such as HSO₃ ¹⁻ or SO₃ ²⁻), as compared to a corresponding activated carbon sorbent including less or substantially no nitrogen in a corresponding particle surface layer under substantially similar conditions.

In various active carbon sorbents, two issues can occur during pollutant capture such as mercury capture: 1) getting high oxidation reactivity at a carbon edge site (kinetic effect) and 2) preventing/avoiding the loss of oxidized mercury from the carbon-bound states as a result of displacement by sulfate (equilibrium effect). Elemental mercury in the gas phase can be oxidized at the carbon edge surface (cationic zigzag sites) and can be bound covalently as an organomercury halide. The cationic sites can be formed by addition of acids or halogens (X₂) to the carbon edge structure, which can result in a carbenium-halide ion pair. The oxidation can be assisted by the negative halide ion stabilizing the developing positive charge on the mercury atom as it adds to the carbenium atom. The oxidation can occur more readily if the oxidation potential (charge) of the carbenium ion or stability thereof is higher, which can be influenced or determined by the adjacent charges present in the carbon framework structure and nearby surroundings. Additional cationic functionality in the structure can raise the oxidation potential (increases positive charge) at the reactive site, or can increase the stability of a positive charge at the reactive site. Negative groups (such as ions derived from SO₃, e.g., SO₃ ²⁻ and SO₂ ¹⁻, can stabilize and lower the overall charge and available carbenium ions and thereby reduce the reactivity for oxidation of the mercury and availability for capture of mercury.

The longer-term equilibrium effect can be less important for capture over a short contact time, such as inflight capture by electrostatic precipitators (ESPs). However, in some situations the equilibrium displacement problem can be more important, e.g., baghouse collection or SO₃ injection or formation in a selective catalytic reduction (SCR) unit. Since sulfate concentrations can increase with time of exposure on the carbon surface, their effect in displacing mercury halides into the gas phase (desorption and breakthrough) can be important in long exposure times. When SO₃ related compounds and ions such as sulfuric acid, sulfate, or related ions, are initially present or form quickly on a wet surface, e.g., with SO₃ injection, the equilibrium displacement effect can also become important in systems with a short contact time.

In various embodiments, the nitrogen in the surface layer can stabilize or increase positive charge in the carbon structure which can overcome depletion of charge by sulfate and the carbon edge can be promoted with a halogen/halide. In some embodiments, the collection of cationic centers in the carbon edge structures (normally present in a halogenated (e.g. brominated) carbon and useful for rapid mercury oxidation) can be impaired by interference of bisulfate ions and other related ions formed from SO₃ reaction at the carbon surface. These anions can neutralize the positive charge of the carbenium ions and lower the overall oxidation potential of the remaining reactive sites that have a shared charge. Additional cationic centers can be generated within the carbon structure by introducing nitrogen atoms during the activated carbon formation, helping to counter this effect and offset some of the charge that can used by ionic or other interactions with, e.g., SO₃ or ions derived from SO₃. Atoms such as nitrogen can be added in the polycyclic structure to form increased cations or to stabilize existing cations.

In some embodiments, the nitrogen in the surface layer of the activated carbon sorbent particles increases the cationic charge in the sorbent because the nitrogen protects the cation centers from SO₃ and ions or compounds derived from SO₃. The nitrogen atoms can form or be part of a charged cage or other protective blocking structure around a carbon edge structure to prevent access by SO₃ and ions or compounds derived from SO₃ such as anionic sulfate groups but allow diffusion of mercury atoms into the nanostructure to reach active centers for oxidation or sorbtion.

In some embodiments, an inorganic matrix support such as clay can help to block active cationic centers from access by SO₃ and ions or compounds derived from SO₃ or can help to stabilize or increase the cationic charge in the active carbon sorbent.

In some embodiments, addition of acid or acidic materials to the activated carbon improves the performance. In various embodiments, acid or acidic materials can be added prior to the use of the carbon by impregnating an acidic solution into the carbon, or can be added as a solution or gas to the sorbent bed during use. The modified carbon can be impregnated with an acidic material, such as about 1 wt % or less or about 2 wt %, 3, 4, 5, 6, 7, 8, 9, 10, 15, or about 20 wt % or more or acidic material, such as HBr, HCl, H₂SO₄, and the like.

Method of Reducing Pollutant Content in a Pollutant-Containing Gas.

In various embodiments, the present invention provides a method of using the activated carbon sorbent. The method can be any suitable method. For example, some embodiments provide a method of reducing the pollutant content in a pollutant-containing gas. In some examples, the pollutant-containing gas can include at least some oxygen. The method can include obtaining or providing an activated carbon sorbent including activated carbon sorbent particles including nitrogen in a surface layer or the sorbet particles. In some embodiments, the concentration of nitrogen in a surface layer of the sorbent particles can be higher than the concentration of nitrogen in a core of the sorbent particles. The activated carbon sorbent can be any activated carbon sorbent including nitrogen described herein. In some examples, the activated carbon sorbent including nitrogen can be a promoted activated carbon sorbent including nitrogen. In some examples, the activated carbon sorbent including nitrogen can be an inorganic matrix-supported or nanocomposite activated carbon sorbent including nitrogen. In some examples, the activated carbon sorbent can be both promoted and an inorganic matrix-supported or nanocomposite activated carbon sorbent including nitrogen. In some embodiments, the activated carbon sorbent can be promoted but include no inorganic matrix support. In some embodiments, the activated carbon sorbent can be neither promoted nor inorganic matrix-supported. The activated carbon sorbent can include binding sites that can bind with at least one of the pollutant in the pollutant-containing gas and an oxidized species of the pollutant, to form the pollutant-sorbent composition. At least a portion of the binding sites in the activated carbon sorbent can react with at least one of the pollutant and an oxidized species of the pollutant, to form the pollutant-sorbent composition.

The method of reducing the pollutant content in a pollutant-containing gas can include contacting a pollutant-containing gas with the activated carbon sorbent. The contacting forms a pollutant-sorbent composition. The contacting can be any suitable contacting. In some embodiments, contacting the pollutant-containing gas with the activated carbon sorbent can include adding or injecting the activated carbon sorbent into the pollutant containing gas. For example, the contacting can occur in the gas. In another embodiment, the contacting can occur in an aqueous liquid. In another example, the contacting can occur in the gas, and subsequently contacting can also occur in an aqueous phase such as a scrubber.

In some embodiments, during the contacting of the pollutant-containing gas with the activated carbon sorbent, the activated carbon sorbent can be in any suitable configuration such that it contacts the pollutant-containing gas. For example, during the contacting, the activated carbon sorbent can be at least one of in a fixed structure such as a fixed bed, in a moving structure such as a moving bed, in a scrubber, in a filter (e.g., a fixed filter or a travelling/moving filter) or suspended in the pollutant-containing gas.

The pollutant-sorbent composition can be any suitable composition including the pollutant or an oxidized or otherwise chemically transformed form of the pollutant and the activated carbon sorbent. In some embodiments, mercury is absorbed in its elemental form by the sorbent; the mercury-sorbent composition can include the sorbent and the elemental form of mercury. In some embodiments, the mercury is converted by the sorbent via a chemical reaction, such as oxidation, such that the mercury from the gas is transformed into an organomercury compound including the carbon framework of the activated carbon bound to mercury, which can be released as a mercury (II) compound upon reaction with a suitable acid to generate the salt thereof. In some embodiments, the mercury-sorbent composition can include at least one of elemental mercury, organomercury compound, and Hg(II) compounds.

In some examples, elemental mercury or transformed mercury can remain absorbed to the sorbent until the mercury-sorbent composition has been removed in a later separation step. For example, elemental mercury or transformed mercury can be absorbed, or reacted and absorbed, into or onto the sorbent composition, such that after separating the pollutant-sorbent composition from the pollutant-containing gas, the separated gas has about 1% or less, 3%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.9%, 99.99%, or about 99.999% or more of the mercury that was originally present in the pollutant-containing gas. In some embodiments, elemental mercury or transformed mercury can be released from the mercury-sorbent composition; for example, less than about 1 wt %, 3 wt %, 5 wt %, 10 wt %, 20 wt %, 30 wt %, 40 wt %, 50 wt %, 60 wt %, 70 wt %, 80 wt %, 90 wt %, 95 wt %, or less than about 99 wt % of the mercury can be released from the mercury-sorbent composition prior to separation of the mercury-sorbent composition from the gas. In some examples, the majority of absorbed elemental or transformed mercury can remain part of the mercury-sorbent composition until the mercury-sorbent composition is removed in a later separation step. In some examples, transformed mercury that is released from the mercury-sorbent composition can be later removed from the gas via the separation step or another step. In some examples, elemental or transformed mercury that has been released from the mercury-sorbent composition can contact activated carbon sorbent to form a mercury-sorbent composition, to be removed later via the separation step.

The method of reducing the pollutant content in a pollutant-containing gas can include separating at least some of the pollutant-sorbent composition from the pollutant-containing gas, to give separated gas. In some embodiments, separating at least some of the pollutant-sorbent composition from the pollutant containing gas includes separating in a particulate separator. The particulate separator can be any suitable particulate separator, such as an electrostatic precipitator (ESP), a baghouse, a wet scrubber, a filter, cyclone, fabric separator, or any combination thereof. In some embodiments, an electrostatic precipitator can be used, followed by a scrubber. In other embodiments, an electrostatic precipitator can be used without a scrubber, or another particulate separator can be used. Some devices that can function as particulate separators can also have other functions, for example a scrubber can also remove SO₂ or SO₃. In embodiments that include contacting of the mercury with a sorbent in an aqueous phase, e.g. in a scrubber, the removal of mercury from the gas that occurs within the aqueous phase by reaction or interaction of the mercury with the sorbent in the aqueous phase can be considered separation of the mercury-sorbent composition from the gas.

In some examples, by separating the particulates from the mercury-containing gas, at least about 20 wt %, 30 wt %, 40 wt %, 50 wt %, 60 wt %, 70 wt %, 80 wt %, 90 wt %, 95 wt %, 96 wt %, 97 wt %, 98 wt %, 99 wt %, 99.9 wt %, 99.99 wt %, or about 99.999 wt % or more mercury can be removed from the mercury-containing gas stream. As discussed herein, the mercury can be removed in the form of elemental mercury, or in the form of a transformed mercury, such as an organomercury compound including the mercury bound to the carbon framework of the activated carbon or as Hg(II) complexed with a suitable counterion.

In some embodiments, at least one of the contacting and the separating occurs in an aqueous scrubber. The aqueous scrubber can be any suitable aqueous scrubber. For example, the scrubber can include an aqueous slurry that includes the activated carbon sorbent.

In some embodiments, the method removes about 1% or less, or about 2%, 3, 4, 5, 10, 20, 30, 40, 50, 60, 70, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.5, 99.9, 99.99, 99.999, or about 99.9999% or more of the mercury present in the mercury-containing gas (e.g. the final concentration of mercury divided by the initial concentration of mercury). In some embodiments, the activated carbon sorbent combines with about 50-100 wt % of the mercury present in the mercury-containing gas, or about 60-90 wt %, 60-80 wt %, 70-80 wt %, 80-90 wt %, 90-100 wt %, or about 95-100 wt % or the mercury present in the mercury-containing gas.

In some embodiments, the concentration of sulfur(VI) in the mercury-containing gas (e.g. from SO₃, H₂SO₄, and the like) is greater than about 3 ppm (by mole) and a first quantity of the activated carbon sorbent forms a mercury-sorbent composition at a first mercury adsorption rate, wherein the first adsorption rate is higher than a mercury absorption rate under substantially similar conditions of the first quantity of a corresponding activated carbon sorbent including at least one of a) less or substantially no nitrogen in a corresponding surface layer, b) less or substantially no halide- or halogen-promotion, and c) less or substantially no inorganic matrix support. In some embodiments, the concentration of SO₃ in the pollutant-containing gas at or near the location wherein the pollutant-containing gas contacts the sorbent is about 1 ppm to about 100,000 ppm, 2-10,000 ppm, 3 ppm-1000 ppm, 3-100 ppm, 3-50 ppm, 3-10 ppm, or about 3-6 ppm or more, or the concentration of sulfur(VI) in the pollutant-containing gas (e.g. from SO₃, H₂SO₄, and the like) at or near the location wherein the pollutant-containing gas contacts the sorbent is about 1 ppm to about 100,000 ppm, 2-10,000 ppm, 3 ppm-1000 ppm, 3-100 ppm, 3-50 ppm, 3-10 ppm, or about 3-6 ppm or more, wherein ppm designates parts per million by mole. The concentration can be an instantaneous concentration, or an average concentration over time. The nitrogen in the surface layer of the activated carbon sorbent particles can decrease neutralization of carbocations in the activated carbon by at least one of SO₃ ²⁻ and HSO₃ ¹⁻, as compared to a corresponding activated carbon sorbent including less or substantially no nitrogen in a corresponding surface layer under substantially similar conditions. The nitrogen in the surface layer of the activated carbon sorbent particles can at least partially block carbocations in the activated carbon from at least one of SO₃ ²⁻ and HSO₃ ⁻¹, as compared to a corresponding activated carbon sorbent including less or substantially no nitrogen in a corresponding particle surface layer under substantially similar conditions.

In some embodiments, the method of reducing the pollutant content in a pollutant-containing gas includes at least one of during and prior to the contacting adding or injecting an alkaline component into the pollutant-containing gas. The alkaline component can be any suitable alkaline component, such as an oxide, hydroxide, carbonate, or phosphate of an alkali element, an alkali or alkaline-earth element, and a compound or material including the same. In various examples, the addition of an alkaline component separately or with the carbon sorbent can result in improved mercury capture. Various factors can impact the effectiveness of the alkaline addition, such as, for example, flue gas pollutants, flue gas constituents (e.g., SO₂, NO_(x), Se, HCl, and the like), operating temperature, mercury form, and mercury concentration. In some examples, the alkaline-to-activated-carbon ratio can be adjusted to optimize for a given set of site conditions.

In some embodiments, the activated carbon includes a stabilizing agent. In some examples, the stabilizing agent can include at least one of S, Se, H₂S, SO₂, H₂Se, SeO₂, CS₂, P₂S₅, or mixtures thereof. The stabilizing agent can be added before or after promotion.

In various embodiments, the rate of mercury removal can decrease gradually with increasing temperature and with increased loading of mercury, at least partially due to the increase in the rate of a reverse reaction. In some examples, the highest rates can occur at about 100 to 150° C., 50-200° C., or about 50-250° C. In some examples, at 400° C., the reverse reaction can be highly favored thermodynamically. In some examples, the activated carbon can be regenerated by washing with water to remove sulfuric acid thereon, such as described in U.S. Pat. No. 8,173,566.

In some embodiments, the method of reducing the pollutant content in a pollutant-containing gas can include regenerating the pollutant-sorbent composition to give a regenerated activated carbon sorbent. The regeneration can be any suitable regeneration that allows the regenerated activated carbon sorbent to be reused for removing pollutant from the pollutant-containing gas. The method can include using the regenerated activated carbon sorbent to remove the pollutant from the pollutant-containing gas.

Method of Making Activated Carbon Including Nitrogen.

In some embodiments, the activated carbon including activated carbon particles including nitrogen is commercially acquired. In other embodiments, the activated carbon including nitrogen is synthesized. For example, the method of reducing the pollutant content in a pollutant-containing gas can include making an activated carbon including nitrogen.

For example, in the method of reducing the pollutant content in a pollutant-containing gas, obtaining or providing the activated carbon sorbent can include obtaining or providing a carbon precursor including nitrogen. The method can also include processing (e.g., heating) the carbon precursor, to provide the activated carbon sorbent. The processing can include any suitable processing. In methods that include heating the carbon precursor, the method can include any other suitable optional step in addition to the heating, such as washing, chemical treatment, or vibration. In some embodiments, the carbon precursor includes a carbonaceous material including carbon and a nitrogenous material including nitrogen. The heating can include heating to about 100° C. to 15,000° C., 200° C. to 10,000° C., 300° C. to 9000° C., or about 400° C. to 8000° C.

The carbonaceous material can be any suitable carbonaceous material. For example, the carbonaceous material can be an organic compound. In some examples, the carbonaceous material includes at least one of brown sugar, barley sugar, caramel, cane sugar, corn syrup, starch, molasses, molasses raffinate (sugar waste product), glucans, galactans, xylans, and a sugar waste product. In some examples, the carbonaceous material includes powdered activated carbon, granular activated carbon, carbon black, carbon fiber, carbon honeycomb or plate structure, aerogel carbon film, pyrolysis char, or an activated carbon or regenerated activated carbon with a mass mean particle size greater than fly ash in a flue gas stream to be treated. The nitrogen can be derived from or part of can be any suitable nitrogenous material. For example, the nitrogenous material can be a nitrogen-containing organic compound, such as a nitrogen-containing heterocycle. In some examples, the nitrogenous material includes indole, quinoxaline, carbazole, isoquinoline, piperazine, quinolone, quinoxaline, diazabicyclooctane, polyacrylonitrile, polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymer, vinylpyrrolidone-acrylic acid copolymer, vinylpyrrolidone-maleic acid copolymer, polyethylenimine, an amino acid (e.g., alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, or valine), analine, nitrobenzene, hydroxylamine, urea, hydrazine, sulfamic acid, nitriles, carbamates, isocyanates, urethanes, or a combination thereof. The nitrogenous material can be any suitable ammonium salt, such as an ammonium salt derived from an aliphatic nitrogen-containing compound, an aromatic amine-containing compound, or a heterocyclic nitrogen-containing compound; in embodiments wherein the nitrogenous material is a halide salt, the activated carbon including nitrogen perform equivalently to an promoted material and a promotion step can be skipped or reduced. In some examples, the nitrogenous material can be at least one of ammonia, ammonium bromide, ammonium chloride, nitric acid, nitrous acid, nitrogen dioxide, compounds including NO₃, compounds including NO₂, and the like.

In one example, the activated carbon including activated carbon sorbent particles including nitrogen can be prepared by surface modification of any kind of activated carbon or char by applying a nitrogen-containing polymer coating or impregnation to the existing carbon or lower temperature char and recarbonizing the impregnated carbon. The coating or impregnation can include a polymer or copolymer containing a nitrogen heterocycle such as a polymerized vinylpyrollidone. In one example of this type of carbon, poly(vinylpyrrolidone), poly(vinylpyrrolidone-co-maleic acid) or poly(vinylpyrrolidone-covinyl acetate) is used to coat the carbon surface. Upon heating or recarbonization, the impregnated mixture can form a nitrogen-containing activated carbon surface layer on the particles. The nitrogen-concentration in the surface layer of the nitrogen-containing activated carbon can be higher than the nitrogen concentration of the material prior to the surface modification or impregnation with nitrogen.

In one example, the activated carbon including nitrogen can be prepared by surface modification of an oxidized char by treatment of the char with a suitable nitrogenous compound, such as ammonia or urea, followed by activation of the nitrogen-impregnated material.

In one example, the activated carbon including nitrogen can be prepared by impregnation of nitrogen containing compounds into a char followed by carbonization and activation of the impregnated char by convention methods. One example carbon of this type is the combination of amines or amino acids with carbohydrates, which combination undergoes the Maillard condensation reaction on heating to form carbon surface containing nitrogen heterocyclics.

In one example, the activated carbon including nitrogen can be prepared by impregnation of a nitrogen containing compound into a coal, lignite, or leonardite, followed by carbonization and activation.

Promoted Activated Carbon Sorbent Including Nitrogen.

In some embodiments, the activated carbon including activated carbon sorbent particles including nitrogen includes a promoted activated carbon sorbent including nitrogen. The activated carbon sorbent including nitrogen used in the method of reducing the pollutant content in a pollutant-containing gas can be a promoted activated carbon sorbent, and can include nitrogen. The method can include promoting an unpromoted activated carbon sorbent, or the promoted sorbent can be commercially acquired.

For example, the method of reducing the pollutant content in a pollutant-containing gas can include obtaining or providing an unpromoted carbon sorbent. The unpromoted carbon sorbent can be any suitable unpromoted sorbent including nitrogen, and can be synthesized or commercially acquired. The method can include obtaining or providing a promoter. The method can include promoting at least a portion of the unpromoted sorbent by contacting (e.g., chemically reacting) the portion of the unpromoted sorbent with the promoter to form the activated carbon sorbent.

The promoter can be any suitable promoter, such that a promoted sorbent is formed that is effective for the removal of pollutants such as mercury from a pollutant-containing gas. For example, the promoter can include a halogen or halide promotor. The halogen or halide can be fluorine or fluoride, chlorine or chloride, bromine or bromide, or iodine or iodide. In some examples, the promotor can include at least one of a halogen, a Group V halide, a Group VI halide, a hydrogen halide, an ammonium halide, an alkali earth metal halide, and an alkaline earth metal halide. Thus, the activated carbon in some embodiments can be at least one of halogen-promoted, Group V halide-promoted, Group VI halide-promoted, hydrogen halide-promoted, ammonium halide-promoted, alkali earth metal halide-promoted, and alkaline earth metal halide-promoted. The promoter can include at least one of HI, IBr, ICl NH₄Br, NaBr, CaBr₂, HBr, NaCl, CaCl₂, and HCl. In some examples, the promoter is NH₄Br, and can be injected into a warm zone in a duct, for example separately or with the activated carbon sorbent. In some examples, any suitable halogen- or halide-containing material, such as NaCl, CaCl₂, NaBr, or CaBr₂ can be injected with the coal during the combustion process, which can activate the carbon. In various embodiments, the halogen- or halide-containing material can transform into an activate promotor such as active bromide or chloride compounds like HCl, HBr, xCl, or xBr. In some examples, the promoter is in a form including at least one of a vapor form, in a solvent, as a liquid, as a solid, and a combination thereof. In some embodiments, the promoting can occur in an aqueous scrubber, wherein the scrubber includes an aqueous slurry that includes the promotor.

The promoting of the sorbent material can occur before addition or injection into a gas stream, during addition or injection into a gas stream, after addition or injection into a gas stream, or a combination thereof, wherein the gas stream can be a mercury-containing gas stream, a transport stream, or a combination thereof. In some examples, the promoter can be added to the sorbent before the promoter and the sorbent react, such that the heat of the gas stream into which the promoter is added causes the promoting of the sorbent. For example, the promoter can be added as a gas, as a gas dissolved in a liquid, or as a solid such as a salt, or other substance (e.g., acid) dissolved in liquid (e.g., water), for example, hydrobromic acid. In examples wherein the promoter is added in a liquid such as water, the water can be allowed to dry, which can allow the promoter to adhere to, impregnate, or react with the activated carbon sorbent, or a combination thereof. In some examples, a pre-added promoter can be an ammonium salt, such as an ammonium chloride, an ammonium bromide, or an ammonium iodide, including, for example, mono-, di-, tri-, or tetraalkyl ammonium halides, or NH₄ ⁺ halide salts. In some examples, the promoter can be added to the sorbent near to or at the time of promoting; for example, the promoter can be added to a gas stream with the sorbent or such that it contacts the sorbent within a heated gas stream, such as a mercury-containing gas stream or a feed gas stream. In some examples, the promoter can be NH₄Br.

In some embodiments, a promoter precursor transforms into the halogen or halide promoter that reacts with the activated carbon sorbent to give the activated carbon material. The promoter precursor can be any suitable precursor that can transform into the halogen or halide promoter. In some embodiments, the promoter precursor can be at least one of on the unpromoted sorbent and added or injected with the unpromoted sorbent. In some embodiments, the promoter can be HBr, and in some examples, the HBr can be provided via degradation or reaction of a promoter precursor such as ammonium bromide, sodium bromide, or calcium bromide. The promoter can be HCl, and in some examples, the HCl can be provided via degradation or reaction of a promoter precursor such as ammonium chloride, sodium chloride, or calcium chloride. The promoter can be HF, and in some examples, the HF can be provided via degradation or reaction of a promoter precursor such as ammonium fluoride, sodium fluoride, or calcium fluoride. In some examples, the promoter (e.g., HBr or HCl) or promoter precursor (e.g., NH₄Br, NaBr, CaBr₂, NH₄Cl, NaCl, CaCl₂)) can be added or injected in the flue gas separately from the activated carbon sorbent or with the activated carbon sorbent (e.g., can be applied to the sorbent pre-injection, added or injected simultaneously at the same location, or added or injected simultaneously at different locations). In some examples, NaCl, CaCl₂, NaBr, or CaBr₂ can be added with uncombusted material such as uncombusted coal.

Inorganic Matrix-Support or Nanocomposites.

In some embodiments, the activated carbon including activated carbon particles including nitrogen includes an inorganic matrix-support or is a nanocomposite. The activated carbon including nitrogen used in the method of reducing the pollutant content in a pollutant-containing gas can include an inorganic matrix-support or can be a nanocomposite. The method can include adding an inorganic matrix-support to the activated carbon or making a nanocomposite using unsupported activated carbon including nitrogen, or the method can include commercially acquiring the matrix-supported or nanocomposite activated carbon. In various embodiments, the inorganic matrix support includes at least one of diatomaceous earth, a clay, a zeolite, or a mineral.

For example, the method of reducing the pollutant content in a pollutant-containing gas can include obtaining or providing a substrate material. The substrate material can be any suitable substrate. For example, the substrate can be at least one of diatomaceous earth, a clay, a zeolite, or a mineral. The method can include contacting the carbon precursor and the substrate material, to provide a sorbent starting material. The contacting can take place in any suitable fashion. The contacting mixes the carbon precursor and the substrate material, such that when the conglomeration is heated (or subjected to any other suitable source of energy), the carbon nanocomposite or supported sorbent is formed. The contacting can be performed such that the carbon precursor is approximately evenly distributed on the substrate. In some examples, water or another solvent can be added to help distribute the carbon precursor on the substrate. In examples where water is included in the mixture of the carbon precursor and the substrate, the conglomeration can be dried prior to the heating. The drying can occur in any conventional manner (e.g., convective, conductive, microwave, and the like), including by heating near or above the boiling point of the solvent, in the case of water (e.g., 50° C.-120° C. or higher), at atmospheric pressure, under pressure, or under a vacuum.

The substrate can include any suitable porous material. For example, the substrate material can be diatomaceous earth, zeolites, porous minerals (e.g., clays) including, for example, smectites (e.g., montmorillonite, bentonite, nontronite, saponite), kaolins, illites, chlorites, sepiolite, or attapulgites. In some examples, the substrate can include polymers, non-metals, metals, metalloids, ceramics or mixtures, and blends, as well as composites and alloys thereof. The materials can be synthetic or naturally occurring or naturally derived materials. Examples of synthetic polymers include any common thermoplastics and thermosetting materials. Examples of metals include aluminum, titanium, copper, steel, and stainless steel. Examples of ceramics include any form of alumina, zirconia, titania, and silica. Examples of naturally occurring or naturally derived materials include wood, wood composites, paper, cellulose acetate, and geologic formations such as granite or limestone. Examples of non-metals include various forms of carbon such as graphite or carbon. Examples of metalloids include silicon or germanium. The porous material can be a construction material such as concrete or asphalt.

In some examples, the substrate material can be present in from about 1 w % to about 99 wt %, about 20 wt % to about 80 wt %, or about 40 wt % to about 60 wt % of the starting material for the carbon nanocomposite sorbent. Wt % in this paragraph refers to the percentage by weight based on the total weight of the carbon precursor and the substrate material.

The method can include processing (e.g., heating, vibrating, sonicating, microwaving, or otherwise adding energy to) the sorbent starting material, to provide the activated carbon sorbent. The contacted composition of the carbon precursor and the substrate can then be processed (e.g., heated, vibrated, sonicated, microwaved, or other suitable addition of energy) to form the carbon nanocomposite or inorganic matrix-supported sorbent. The processing can take place at any suitable temperature, such that the sorbent is sufficiently formed, for example heating to about 50° C., 100° C., 200° C., 300° C., 400° C., 500° C., 600° C., 700° C., 800° C., 900° C., 1000° C., 1100° C., or about 1200° C. or higher. The processing can take place for any suitable time, such that the carbon nanocomposite is sufficiently formed, for example, greater than about 1 min, 2 min, 5 min, 10 min, 30 min, 1 h, 1.5 h, 2 h, 3 h, 4 h, 5 h, 10 h, or greater than about 24 h. The heating can take place in any suitable apparatus, for example, a unit that substantially excludes oxygen, e.g., that allows heated inert gas air to flow around the mixture being heated. In one example, the heating occurs in a furnace having an inert gas environment therein. The processing can be accelerated, or lengthened, depending on the apparatus and the nanocomposite or supported material.

In some embodiments, heating the sorbent starting material can provide a second sorbent starting material. The method can further include reacting the second sorbent starting material with an acidic or basic material, to provide the activated carbon sorbent. The acidic or basic material can be any suitable acidic or basic material, such as HBr, HCl, H₂SO₄, KOH, NaOH, and the like. In some embodiments, treatment with an acidic or basic material can prepare the activated carbon for treatment with a promotor or can prepare the material such that sufficient reactivity or absorption with mercury or another pollutant is obtained.

Method of Making an Active Carbon Sorbent Including Nitrogen.

In various embodiments, the present invention provides a method of making an activated carbon sorbent including activated carbon sorbent particles including nitrogen. Embodiments of the present invention can include any activated carbon sorbent including nitrogen made by the method. The method includes obtaining or providing unpromoted sorbent including nitrogen. The unpromoted sorbent including nitrogen can be any suitable activated carbon sorbent including nitrogen, such as any activated carbon sorbent including nitrogen described herein. The unpromoted sorbent including nitrogen can be acquired commercially or can be synthesized. The method can include promoting at least a portion of the unpromoted sorbent. The promoting can include contacting (e.g., chemically reacting) the portion of the unpromoted sorbent with a promoter to form an activated carbon sorbent including activated carbon sorbent particles including nitrogen.

In some examples, the unpromoted sorbent including nitrogen can include an inorganic matrix support or can be a nanocomposite. For example, the method of making an activated carbon sorbent including nitrogen can include obtaining or providing a carbon precursor including nitrogen. The method can include obtaining or providing a substrate material. The method can include contacting the carbon precursor and the substrate material to provide a sorbent starting material. The method can also include heating the sorbent starting material to provide the unpromoted carbon sorbent including nitrogen. The unpromoted sorbent including nitrogen can include activated carbon sorbent particles including nitrogen.

In some embodiments, the method of making an activated carbon sorbent including nitrogen can include synthesizing the carbon precursor including nitrogen from carbonaceous and nitrogenous materials. For example, the method can include obtaining or providing a carbonaceous material including carbon and a nitrogenous material including nitrogen. The method can include suitably contacting and processing the carbonaceous material and the nitrogenous material, wherein processing can including at least one of heating, microwaving, sonication, vibration, and the like, to provide the carbon precursor including nitrogen.

EXAMPLES

The present invention can be better understood by reference to the following examples which are offered by way of illustration. The present invention is not limited to the examples given herein.

Example 1. Impregnation of Nitrogen Precursors into a Char Followed by Carbonization and Activation of the Impregnated Char Example 1a. Carbon Precursor

A carbon (20×60 mesh) prepared by steam activation of a lignite char was stirred with an aqueous solution of dextrose and ethanolamine in ratio of 1 part of carbon to 0.016 parts of ethanolamine and 0.034 parts of dextrose. The water solvent was removed by rotovaporation and the impregnated carbon was air-dried. The dried material was reactivated at 750° C. for 2 hours under nitrogen stream.

Example 1b. Char Precursor

A char (20×60 mesh) prepared by heating a lignite at 400° C. was stirred with an aqueous solution of dextrose and ethanolamine in ratio of 1 part of carbon to 0.016 parts of ethanolamine and 0.034 parts of dextrose. The water solvent was removed by rotovaporation and the impregnated carbon was air-dried. The dried material was activated at 750° C. for 2 hours under nitrogen stream.

Example 1c. Wood Charcoal Precursor

A carbon (20×60 mesh) prepared by steam activation of a wood char was stirred with an aqueous solution of dextrose and ethanolamine in ratio of 1 part of carbon to 0.016 parts of ethanolamine and 0.034 parts of dextrose. The water solvent was removed by rotovaporation and the impregnated carbon was air-dried. The dried material was reactivated at 750° C. for 2 hours under nitrogen stream.

Example 1d. Wood Charcoal—Alanine

A carbon (20×60 mesh) prepared by steam activation of a wood char was stirred with an aqueous solution of dextrose and alanine in ratio of 1 part of carbon to 0.016 parts of ethanolamine and 0.034 parts of alanine. The water solvent was removed by rotovaporation and the impregnated carbon was air-dried. The dried material was reactivated at 750° C. for 2 hours under nitrogen stream.

Example 2. Tube Reactor Testing

The molecular sieve carbons obtained as described in Examples 1a-d were impregnated with 5 wt % of sulfuric acid. The impregnated carbon was then dried in an oven at 110° C. The carbon (0.100 g) was packed into a 3 mm diameter pyrex tube and held in place by glass wool plugs at both ends. A constriction in the pyrex tube at exit end prevented the plug from blowing out. The reactor tube was heated in a GC oven at 150° C.±0.50 as a constant temperature device. The mercury vapor was contained in an air flow of 100 cm³/min through the reactor tube at a concentration of 429-447 micrograms/m³, determined with a continuous mercury vapor monitor.

The mercury source was a temperature-calibrated permeation tube. The permeation tube was heated in a double-jacketed glass condenser with a circulating hot silicone oil system. The concentration in the effluent air stream from the reactor tube was monitored with a continuous cold-vapor UV mercury vapor monitor (EPM). Blank runs were conducted before each carbon test to determine the mercury concentration. The instrument was zeroed with an air stream passed through a large iodized carbon filter. This apparatus thus gave the percent of mercury not removed by the carbon bed (the concentration of mercury in the outlet divided by the concentration of mercury in the inlet, times 100). For the nitrogenous molecular sieve carbons (examples 1-4) only 1% of the mercury vapor was not removed by the carbon bed over a period of several hours.

Example 3. Filter Bed Testing

The sorbent carbon pretreated as in Example 1e was ground to about 200 mesh and introduced into a tube where it could be drawn by reduced pressure onto a teflon or quartz filter held in a stainless steel holder. The carbon-impregnated filter and holder were then placed in the oven under air flow and tested as described in Example 2.

Examples 4. Impregnation of Nitrogen-Containing Polymers into an Activated Carbon or Char Followed by Carbonization and Activation of the Impregnated Material Example 4a. Vinylpyrrolidone-Acrylic Acid Copolymer

A carbon prepared by steam activation of a lignite was stirred with an aqueous solution of poly(vinylpyrrolidone-co-acrylic acid) for 30 min. The amount of the polymer was selected to provide loadings of 1% to 30% by weight. The solvent was evaporated by rotovaping at 50° C. and further dried in an oven at 110° C. The impregnated carbon was reactivated by heating at 750° C. for 2 hours in a stream of nitrogen. Approximately 40% of the polymer weight was converted to surface coating and 60% was volatilized.

Example 4b. Vinylpyrrolidone-Vinyl Acetate Copolymer

An activated carbon was impregnated with poly(vinylpyrrolidone-co-vinyl acetate) dissolved in dichloromethane. The solvent was evaporated and the impregnated carbon died in an oven at 110° C. The impregnated carbon was then activated by heating at 750° C. for 2 hours in a nitrogen stream.

Example 4c. Poly(vinylpyrrolidone)

An activated carbon was impregnated with one of poly(vinylpyrrolidone) and the copolymers described in Examples 4a-b and activated as described in Example 4a.

Example 4d. Poly(vinylpyrrolidone)

A KOH-activated lignite was impregnated with one of polyvinylpyrrolidone and and the copolymers described in Examples 4a-4b and activated as described in Example 4a.

Example 4e. Wood-Derived Charcoal

Wood-derived charcoal was impregnated with one of poly(vinylpyrrolidone) and the copolymers described in Examples 4a-4b and activated as described in Example 4a.

Example 4f. Carbonization of a Lignite. (Hypothetical Example)

Chars are produced by carbonization of a lignite, impregnated by one of poly(vinylpyrrolidone) and the copolymers described in Examples 4a-4b, and activated as described in Example 4a. As an alternative, steam activation can be used.

Example 4g. Steam Activation

Examples 4a-4e were carried out using steam activation of the carbon material impregnated with nitrogen-containing polymers to generate effective sorbents.

Example 5. Impregnation of Nitrogen Precursors into a Coal, Lignite, or Leonardite, Followed by Carbonization and Activation of the Impregnated Material Example 5a. 1.4-Diazabicyclo[2.2.2]octane (DABCO)

Lignite (as received) was stirred with an aqueous solution of DABCO in a ratio of 1 part of coal to 0.02 parts of DABCO. The water solvent was removed by filtration, and the impregnated coal was air-dried. The dried material was carbonized at 400° C. and activated at 750° C. for 2 hours under a nitrogen stream.

Example 5b. Sulfamic Acid

Lignite (as received) was stirred with an aqueous solution of sulfamic acid in a ratio of 1 part of coal to 0.02 parts of sulfamic acid. The water solvent was removed by filtration, and the impregnated coal was air-dried. The dried material was carbonized and activated at 750° C. for 2 hours under a nitrogen stream.

Example 5c. Carbonized Lignite

Lignite was carbonized at 400° C. for 30 minutes, and the resulting char was treated by stirring with sulfamic acid solution as described in Example 5b. The treated char was then activated as described in Example 5b.

Example 5d. Steam Activation

Steam activation of the DABCO or sulfamic acid-impregnated chars was also effective in producing mercury sorbent carbons.

Example 6. Preparation of Nitrogen-Containing Pitches

Nitrogen-containing pitches were prepared using a procedure reported by Mochida et al. (Mochida, I.; An, K. H.; Korai, Y. Carbon 1995, 33, 1069). Preparations are summarized in Table 1. As an example, a mixture of isoquinoline (26 g, 0.2 mole), anhydrous aluminum(III) chloride (13.3 g, 0.25 mole), and nitrobenzene (7.68 g, 0.06 mole) was placed in a two-necked flask equipped with a reflux condenser and a nitrogen inlet tube. The mixture was refluxed at 280° C. for 4 hours. The residue was extracted with 0.1 N hydrochloric acid and filtered. The residue was washed with 0.1 N hydrochloric acid. The residue was further extracted with methanol to remove any monomer. The methanol-insoluble pitch was dried in vacuo. The yield of the pitch was 49/o. A portion of the nitrogen-containing pitches were carbonized using Procedure A or B in a nitrogen stream, as described in Example 7.

TABLE 1 Preparation of nitrogen-containing pitches. Catalyst Substrate (g, Cocatalyst Temperature Time Yield Soluble (g, mole) mole) (g, mole) (° C.) (hr) (g, %) (%) Indole None None 253* 4  9.6 Methanol (10, 0.77) (96%) (100) Quinoxaline AlCl₃ Nitrobenzene 225* 4 13.5 EDA** (26, 0.2) (13.3, (7.68, 0.06) (52%) 0.1) Carbazole AlCl₃ Nitrobenzene 25 12 59.1 EDA** (16.7, 0.1) (27.7, (3.6, 0.03) (92%) 0.2) Isoquinoline AlCl₃ Nitrobenzene 280  4  6.5 EDA** (26, 0.2) (13.3, (7.68, 0.06) (25%) 0.1) *indicates reactions carried out in 300-mL Parr reactor. **indicates ethylenediamine.

Several modifications of the method were utilized for the quinoline polymerization. In addition to the flask method, a Parr reactor was used for the reaction, and temperatures and reaction times were varied. The yields are reported in Table 2. In this procedure, 64.5 g of quinoline and 33.25 g of aluminum(III) chloride were placed in a 300-mL Parr autoclave. The reactor was sealed under nitrogen and heated at 280° C. for 4 hours. The hard black mass was extracted with 0.1 N hydrochloric acid followed by extraction with methanol and drying in vacuo. In order to determine the solubility of the polymer, a 10-g portion of this black mass was extracted with 100 mL of ethanol. Extraction data showed that 27 wt % of the product dissolved in ethanol.

TABLE 2 Preparation of nitrogen-containing pitches. Quinoline AlCl₃ Temp. Time Yield Ethanol-S Ethanol-I (g) (g) (° C.) (hr) (g, %) (g) (g) 64.5 33.25 280 12 57.7 — — (89%) 64.5* 33.25 175 12 0  — —  (0%) 64.5* 33.25 280 12 59.1 — — (92%) 64.5* 33.25 280 4 56.8 7.3** 2.7 (88%) (73%) (27%) *indicates reactions carried out in 300-mL Parr reactor. **indicates 10 g of pitch was extracted with ethanol.

Example 7. Preparation of Nitrogen-Impregnated Carbon

Impregnations and recarbonizations were performed to investigate the effects of precursor concentration, activation procedure, and sorbent particle size on mercury sorption. The precursor base carbon, granular activated carbon (Calgon F400 or Gascoyne AC, 20×60) was impregnated with various nitrogen-containing polymers and pitches using an incipient wetness method, described below. For the fine-particle sorbent tests in flue gas compositions, the Calgon carbon was ground to about a 400 mesh size prior to impregnation. The nitrogen polymers such as vinylpyrrolidone polymers and copolymers are commercially available. The urea, alanine-dextrose, piperazine-dextrose, and polyethylenimine-dextrose compositions were prepared similarly.

In a typical procedure for the incipient wetness method, the desired amount of polymer or pitch dissolved in an appropriate solvent was added to the carbon slowly with thorough mixing. The paste was dried to remove solvent. The dried product was packed in a stainless steel tube and activated in a gentle flow of nitrogen using procedure A or procedure B.

Procedure A included: Heated from 25° C. to 400° C. at 10° C./min; held at 400° C. for 30 min; heated from 400° to 750° C. at 20° C./min; and held at 750° C. for 4 hr.

Procedure B included: Heat from 25° C. to 225° C. at 15° C./min; heated from 225° C. 270° C. at 1° C./min; held at 270° C. for 1 hr; cooled to room temperature; heated up to 750° C. at 15° C./min; and held at 750° C. for 4 hr.

Example 8. Preparation of Nitrogen-Containing Carbons from Insoluble Fractions

Insoluble fractions of pitches described in Table 1 were converted into nitrogen-containing carbons by heating in a gentle flow of nitrogen using Procedure B as described above. The resulting carbons were porous glassy materials, similar to cokes.

Example 9. Preliminary Screening of Sorbents Made Using the Nitrogen Containing Materials of Examples 6-7 for Mercury Capture Example 9a. Simulation of the Sulfuric Acid Accumulation

Capture of SO₃ and subsequent sulfuric acid formation on the surface of the nitrogen containing carbons in the hot flue gas stream was simulated by adding 5 wt % sulfuric acid by the incipient wetness method. The acid-impregnated carbons were dried at 110° C.

Example 9b. Packed-Bed Tests

Packed-bed tests in airflow were conducted on the granular carbon products to evaluate the effects of surface modification. The mercury sorption was tested in a flow-through tubular reactor system equipped with continuous in-line mercury analysis of the effluent from the bed to determine mercury removal rates as a function of time. Integration of breakthrough volumes allows determination of mercury sorption per unit mass carbon (mg/g). Air with an elemental mercury concentration of 56 or 81 μg/m³ was passed through the heated (150° C.) reactor. To obtain this concentration, the mercury source was placed in a double-jacketed glass condenser and heated to the desired temperature by pumping hot oil through the condenser.

A glass tube with constriction and glass wool plug was used as the reactor for the mercury sorption tests. A gas chromatography (GC) oven was used as a constant temperature (150° C.) chamber for the reactor. Before the actual test, a blank test was run. The glass tube was attached to the source and the mercury analyzer by Teflon tubes. Mercury vapors diluted with air (2000-4000 cm³/min or 4-8 scfh measured at the detector end) were passed through the tube. The mercury analyzer (Environmental and Process Monitoring [EPM] continuous vapor monitor) was interfaced to a Hydra and personal computer (PC) to record the data. For the packed-bed tests, impregnated activated carbons (20×60-mesh size) were used. In an actual test, about 0.2-0.6 g of sorbent was packed in the glass tube and held by glass wool plugs on both ends. The tests were conducted with a source temperature of 150° C., an oven temperature of 150° C., and an airflow=4 or 8 scfh (4000 cm³/min). Numerous tests were performed at 4000 cm³/min (8 scfh) with carbons prepared by impregnation of various nitrogen compounds, polymers, and pitches into a base Calgon carbon (Tables 3 and 4). These conditions gave partial breakthroughs for the sorbents and allowed comparisons of their kinetic activities.

TABLE 3 Sorbent testing of surface-treated carbons for mercury removal at 8 scfh. Airflow = 4000 cm³/min (8 scfh), over temperature = 150° C., mercury concentration = 81 μg/m³. Recarbon- H₂SO₄ % Hg removed (time, min) Carbon ization Impreg- End of source method nation Initial 50% test Blank — 0 <1 — (0) Calgon 5% 87  50 38 (0) (171)  (304)  Calgon/urea A 5% 95  50 49 (0) (305)  (306)  EERC*/urea A 5% 100  50 38 (0) (575)  (1221)  Calgon/2% A 5% 92  50 39 sulfamic acid (0) (226)  (1303)  Calgon/5% PVP A 5% 94  50 42 (0) (2217)  (2574)  Calgon/10% PVP A 5% 88  50 55 (0) (150)  (253)  Calgon/10% PVP A 5% 90  50 65 (0) (300)  (1098)  Calgon/5% PVP A 5% 98  50 43 (0) (3315)  (4010)  Calgon/2% PVP A 5% 79  50 49 (0) (312)  (320)  Calgon/10% PVP A 5% 85  50 30 (0) (424)  (1114)  Calgon/5% A 5% 90  50 39 vinylpyrrolidone- (0) (84) (180)  vinyl acetate copolymer Calgon/5% A 5% 90  50 29 vinylpyrrolidone- (0) (76) (362)  acrylic acid copolymer Calgon/5% A 5% 98  50 50 vinylpyrrolidone- (0) (223)  (223)  acrylic acid copolymer Calgon/ A 5% 88  50 22 polyethylenimine (0) (373)  (1147)  Calgon/dextrose + A 5% 88  50 35 polyethylenimine (0) (51) (350)  Calgon/dextrose + A 5% 88  50 53 alanine (0) (76) (216)  Calgon/dextrose + A 5% 65  50 25 piperazine (0) (35) (942)  *indicates that the activated carbon was prepared in Example 4a.

TABLE 4 Sorbent testing of nitrogenous pitch-impregnated carbons for mercury capture. Recarbonization procedure B was used for all samples. Sorbent = 0.20 g, particle size = 20 × 50 mesh, airflow = 8 scfh (4000 mL/min), source temperature = 150° C., oven temperature = 150° C. Mercury File H₂SO₄ Concentration % Hg removed (time, min) name Sorbent (g) (wt %) (μg/m³) Initial 50% Final RKS32 None — 81 — 50 — <1 RKS35 Calgon/5 wt % 5% — 89 50 49 quinolone*  (0) (306)  (308)  RKS23 Calgon/5 wt % 5% — 91 50 46 quinolone*  (0) (204)  (292)  RKS37 Calgon/5 wt % 5% — 90 50 25 quinoxaline  (0) (632)  (1300)  RKS31 Calgon/5 wt % 5% — 90 54 34 isoquinoline  (0) (584)  (1214)  RKS75 Calgon/5 wt % 5% — 98 50 49 indole  (0) (1403)  (1473)  *indicates pitch obtained from heating quinolone and aluminum(III) chloride in Parr reactor was dissolved in ethanol and impregnated on Calgon carbon. **indicates pitch obtained from refluxing of quinolone with aluminum(III) chloride was dissolved in EDA and impregnated on Calgon carbon.

Example 9c. Test Results

Carbons prepared by impregnation of urea or sulfamic acid into the Calgon base carbon and recarbonization gave initial capture rates of 95% or 92%, respectively. These results are significantly better than those observed with the unmodified Calgon carbon. Testing the urea carbon at lower temperature (75° C.) gave 100% initial capture. Carbons prepared by impregnation of a nitrogen-containing polymer were highly active in these tests. The sorbent prepared by impregnation of 5 wt % PVP and activated using procedure A (fast heating rate) demonstrated superior activity. The initial removal was 94%, and the decrease to 50% removal required 2217 min. Thus this sorbent retains its high activity far longer than the urea carbon. The sorbent prepared using 10% PVP (also Procedure A) was less active (initially 88% removal, decreasing to 50% at 150 min.

Using procedure B (slower heating rate) gave more active sorbent at the 10% PVP concentration level. Another set of carbons was prepared with different concentrations using Procedure B. Again, the impregnation with 5% concentration of PVP resulted in high activity (initially 98% removal, decreasing to 50% at 3315 mm). The 10% PVP was again less active, and the 2% PVP concentration was the least active.

The carbons prepared from the copolymers of PVP were also prepared and evaluated. The copolymer with vinyl acetate (PVPcoVA) impregnated at 5% concentration (Procedure A) gave a sorbent with relatively low activity. The poly(vinylpyrrolidone-co-acrylic acid) (PVPcOAA) at 5% also gave a low activity sorbent. Using Procedure B for activation improved the activity slightly.

Another type of N-polymer-impregnated carbon was prepared using polyethylenimine. This polymer precursor contains nitrogen in the polymer backbone, in contrast to the PVP where the nitrogen is attached to the carbon chain backbone. The activity was similar to that of the 10% PVP polymers.

Several carbons were prepared by impregnating mixtures of dextrose and amines. None of these exhibited high activities in these tests. Previous tests showed that the dextrose+alanine-impregnated carbon (Procedure B) was fairly active. Since Procedure A was used in the present study, decreases in activity might be related to the fast heating rate used. It may be quite beneficial to perform the reaction slowly in preparing sorbents from these precursors.

The sorbents prepared by impregnation of the nitrogenous pitches prepared by polymerization of various heterocyclics were all fairly active (Table 4), but significant differences in activity were observed. The N-carbon prepared from impregnation of quinoxaline pitch was 2-3 times more active than the quinoline-derived N-carbon. The activity of the isoquinoline-derived carbon was also very high. The high activity of the indole-derived carbon was also of great interest. It is an important lead since indoles are more readily available than the quinoxaline precursors.

Testing was also conducted on the carbonized pitches prepared from the insoluble fractions of the nitrogenous pitches. The activities of the carbonized pitches were very poor. Initial breakthrough was substantial, with percent removals of 21% to 54%, possibly related to the the glassy nature of the carbonized pitches. Although the surface areas were not determined, they may be very low, since the materials did not resemble activated carbons but, rather, cokes.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those of ordinary skill in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

ADDITIONAL EMBODIMENTS

The present invention provides for the following exemplary embodiments, the numbering of which is not to be construed as designating levels of importance:

Embodiment 1 provides a method of reducing the pollutant content in a pollutant-containing gas, the method comprising: obtaining or providing an activated carbon sorbent comprising activated carbon sorbent particles comprising nitrogen in a surface layer of the sorbent particles; contacting a pollutant-containing gas with the activated carbon sorbent, to form a pollutant-sorbent composition; and separating at least some of the pollutant-sorbent composition from the pollutant-containing gas, to give a separated gas.

Embodiment 2 provides the method of Embodiment 1, wherein the pollutant comprises mercury, and the pollutant-containing gas is a mercury-containing gas.

Embodiment 3 provides the method of any one of Embodiments 1-2, wherein the concentration of nitrogen in the surface layer of the sorbent particles is higher than the concentration of nitrogen in a core of the sorbent particles.

Embodiment 4 provides the method of any one of Embodiments 2-3, wherein the activated carbon sorbent combines with at least about 70 wt % of the mercury present in the mercury-containing gas.

Embodiment 5 provides the method of any one of Embodiments 2-4, wherein the mercury-containing gas further comprises a concentration of sulfur(VI) and the concentration of sulfur(VI) in the mercury-containing gas is greater than about 3 ppm by mole and the activated carbon sorbent forms a mercury-sorbent composition at a higher absorption rate relative to a corresponding activated carbon sorbent comprising at least one of a) less or substantially no nitrogen in a corresponding particle surface layer, b) less or substantially no halide- or halogen-promotion, wherein the activated carbon sorbent comprising the activated carbon sorbent particles is halide- or halogen-promoted, and c) less or substantially no inorganic matrix support, wherein the activated carbon sorbent comprising the activated sorbent particles is inorganic matrix-supported.

Embodiment 6 provides the method of any one of Embodiments 1-5, wherein the pollutant-containing gas further comprises a concentration of sulfur(VI) and the concentration of sulfur(VI) in the pollutant-containing gas is about 3 ppm-2000 ppm.

Embodiment 7 provides the method of any one of Embodiments 1-6, wherein the nitrogen is substantially homogenously distributed in the core of the activated carbon sorbent particles.

Embodiment 8 provides the method of any one of Embodiments 1-7, wherein the nitrogen in the surface layer decreases neutralization of carbocations in the activated carbon by at least one of SO₃ ²⁻ and HSO₃ ¹⁻, as compared to a corresponding activated carbon sorbent comprising less or substantially no nitrogen in a corresponding particle surface layer.

Embodiment 9 provides the method of any one of Embodiments 1-8, wherein the nitrogen in the surface layer at least partially blocks carbocations in the activated carbon from at least one of SO₃ ²⁻ and HSO₃ ¹⁻, as compared to a corresponding activated carbon sorbent comprising less or substantially no nitrogen in a corresponding particle surface layer.

Embodiment 10 provides the method of any one of Embodiments 1-9, further comprising: obtaining or providing an unpromoted carbon sorbent; obtaining or providing a promoter; and promoting at least a portion of the unpromoted sorbent by contacting the portion of the unpromoted sorbent with the promoter to form the activated carbon sorbent.

Embodiment 11 provides the method of Embodiment 10, wherein the promoter comprises a halogen or halide promoter.

Embodiment 12 provides the method of any one of Embodiments 10-11, wherein the promoter comprises at least one of a halogen, a Group V halide, a Group VI halide, a hydrogen halide, an ammonium halide, an alkali earth metal halide, and an alkaline earth metal halide.

Embodiment 13 provides the method of any one of Embodiments 10-12, wherein the promoter comprises at least one of HI, IBr, ICl NH₄Br, NaBr, CaBr₂, HBr, NaCl, CaCl₂, and HCl.

Embodiment 14 provides the method of any one of Embodiments 10-13, wherein the promoter is in a form comprising at least one of a vapor form, in a solvent, as a liquid, as a solid, and a combination thereof.

Embodiment 15 provides the method of any one of Embodiments 10-14, wherein the promoting occurs in an aqueous scrubber, wherein the scrubber comprises an aqueous slurry that comprises the promotor.

Embodiment 16 provides the method of any one of Embodiments 1-15, wherein contacting the pollutant-containing gas with the activated carbon sorbent comprises adding the activated carbon sorbent into the pollutant-containing gas.

Embodiment 17 provides the method of any one of Embodiments 1-16, wherein the activated carbon sorbent is at least one of in a fixed bed, in a moving bed, in a scrubber, in a filter, or suspended in the pollutant-containing gas.

Embodiment 18 provides the method of any one of Embodiments 1-17, wherein the core of the activated carbon sorbent particles comprise about 0 wt %-about 99 wt % nitrogen.

Embodiment 19 provides the method of any one of Embodiments 1-18, wherein the core of the activated carbon sorbent particles comprise about 1 wt %-about 6 wt % nitrogen.

Embodiment 20 provides the method of any one of Embodiments 1-19, wherein the surface layer of the activated carbon sorbent particles comprises about 0.001 wt %-about 99 wt % nitrogen.

Embodiment 21 provides the method of any one of Embodiments 1-20, wherein the surface layer of the activated carbon sorbent particles comprises about 5 wt %-about 80 wt % nitrogen.

Embodiment 22 provides the method of any one of Embodiments 1-21, wherein the surface layer of the activated carbon sorbent comprises a layer at the surface of the particle having a thickness of about 0.001% to about 99% of the radius of the particles.

Embodiment 23 provides the method of any one of Embodiments 1-22, wherein the surface layer of the activated carbon sorbent particles comprises a layer at the surface of the particles having a thickness of about 0.001% to about 50% of the radius of the particles.

Embodiment 24 provides the method of any one of Embodiments 1-23, wherein the activated carbon sorbent particles have an average diameter of about 0.1 μm to about 1000 μm.

Embodiment 25 provides the method of any one of Embodiments 1-24, wherein the surface layer of the sorbent particles is a continuous surface layer.

Embodiment 26 provides the method of any one of Embodiments 1-25, wherein obtaining or providing the activated carbon sorbent comprises: obtaining or providing a carbon precursor comprising nitrogen; and processing the carbon precursor with at least one of heating, microwaving, and irradiating, to provide the activated carbon sorbent.

Embodiment 27 provides the method of Embodiment 26, wherein the carbon precursor comprises a carbonaceous material comprising carbon and a nitrogenous material comprising nitrogen.

Embodiment 28 provides the method of Embodiment 27, wherein the carbonaceous material comprises at least one of brown sugar, barley sugar, caramel, cane sugar, corn syrup, starch, molasses, a glucan, a galactan, a xylan, and a sugar waste product.

Embodiment 29 provides the method of any one of Embodiments 27-28, wherein the nitrogenous material comprises a nitrogen-containing organic or inorganic compound.

Embodiment 30 provides the method of any one of Embodiments 27-29, wherein the nitrogenous material comprises a nitrogen heterocycle, a nitrogen-containing polymer or copolymer, a nitrile, a carbamate, an amino acid, nitrobenzene, hydroxylamine, urea, hydrazine, sulfamic acid, or a combination thereof.

Embodiment 31 provides the method of any one of Embodiments 26-30, further comprising: obtaining or providing a substrate material; contacting the carbon precursor and the substrate material, to provide a sorbent starting material; and processing the sorbent starting material with at least one of heating, microwaving, and irradiating, to provide the activated carbon sorbent.

Embodiment 32 provides the method of Embodiment 31, wherein heating the sorbent starting material provides a second sorbent starting material, further comprising reacting the second sorbent starting material with an acidic or basic material, to provide the activated carbon sorbent.

Embodiment 33 provides the method of any one of Embodiments 31-32, wherein the substrate comprises at least one of diatomaceous earth, a clay, a zeolite, or a mineral.

Embodiment 34 provides the method of any one of Embodiments 31-33, wherein heating the sorbent starting material comprises heating to about 100° C.-about 1200° C.

Embodiment 35 provides the method of any one of Embodiments 31-34 wherein the activated carbon sorbent comprises a carbon nanocomposite sorbent.

Embodiment 36 provides the method of any one of Embodiments 1-35, wherein the activated carbon sorbent comprises one or more binding sites.

Embodiment 37 provides the method of Embodiment 36, wherein at least a portion of the binding sites in the activated carbon sorbent react with at least one of the pollutant and the oxidized species of the pollutant, to form the pollutant-sorbent composition.

Embodiment 38 provides the method of any one of Embodiments 1-37, wherein the separating at least some of the pollutant-sorbent composition from the pollutant containing gas comprises separating in a particulate separator.

Embodiment 39 provides the method of Embodiment 38, wherein the particulate separator comprises an electrostatic precipitator (ESP), a baghouse, a wet scrubber, a filter, cyclone, fabric separator, or any combination thereof.

Embodiment 40 provides the method of any one of Embodiments 10-39, wherein a promoter precursor transforms into the halogen or halide promoter which then reacts with the activated carbon sorbent to give the activated carbon material.

Embodiment 41 provides the method of Embodiment 40, wherein the promoter precursor is at least one of on the unpromoted sorbent and added with the unpromoted sorbent.

Embodiment 42 provides the method of any one of Embodiments 1-41, further comprising at least one of during and prior to the contacting adding an alkaline component into the pollutant-containing gas.

Embodiment 43 provides the method of Embodiment 42, wherein the alkaline component comprises at least one of an oxide, hydroxide, carbonate, or phosphate of an alkali element, an alkali or alkaline-earth element, and a compound or material including the same.

Embodiment 44 provides the method of any one of Embodiments 1-43, wherein the activated carbon sorbent comprises a stabilizing agent comprising at least one of S, Se, or mixtures thereof.

Embodiment 45 provides the method of any one of Embodiments 1-44, wherein the activated carbon sorbent comprises a stabilizing agent comprising at least one of H₂S, SO₂, H₂Se, SeO₂, CS₂, P₂S₅, or mixtures thereof.

Embodiment 46 provides the method of any one of Embodiments 1-45, further comprising regenerating the pollutant-sorbent composition to give a regenerated activated carbon sorbent.

Embodiment 47 provides the method of any one of Embodiments 1-46, wherein the activated carbon sorbent is a generated activated carbon sorbent

Embodiment 48 provides the method of any one of Embodiments 1-47, wherein at least one of the contacting and the separating occurs in an aqueous scrubber.

Embodiment 49 provides the method of Embodiment 48, wherein the scrubber comprises an aqueous slurry that comprises the activated carbon sorbent.

Embodiment 50 provides a method for reducing the mercury content of a mercury-containing gas, the method comprising: obtaining or providing a carbon precursor comprising nitrogen; obtaining or providing a substrate material; contacting the carbon precursor and the substrate material, to provide an inorganic matrix-supported sorbent starting material; heating the inorganic matrix-supported sorbent starting material, to provide an unpromoted sorbent; promoting at least a portion of the unpromoted sorbent by chemically reacting the portion of the unpromoted sorbent with a promoter to form a promoted inorganic matrix-supported activated carbon sorbent comprising activated carbon sorbent particles comprising nitrogen in a surface layer of the sorbent particles; contacting a mercury-containing gas with the activated carbon sorbent, to form a mercury-sorbent composition; and separating at least some of the mercury-sorbent composition from the mercury-containing gas, to give a separated gas; wherein the mercury-containing gas has a concentration of sulfur(VI) of about 3-2000 ppm by mole and a first quantity the activated carbon sorbent forms a mercury-sorbent composition at a first mercury adsorption rate, wherein the first adsorption rate is higher than a mercury absorption rate of the first quantity of a corresponding activated carbon sorbent comprising at least one of a) less or substantially no nitrogen in a corresponding particle surface layer, b) less or substantially no halide- or halogen-promotion, and c) less or substantially no inorganic matrix support.

Embodiment 51 provides a method of making an activated carbon sorbent, comprising: obtaining or providing an unpromoted carbon sorbent comprising nitrogen; promoting at least a portion of the unpromoted sorbent by contacting the portion of the unpromoted sorbent with a promoter to form an activated carbon sorbent comprising activated carbon sorbent particles comprising nitrogen, wherein the concentration of nitrogen in a surface layer of the sorbent particles is higher than the concentration of nitrogen in a core of the sorbent particles.

Embodiment 52 provides the method of Embodiment 51, further comprising: obtaining or providing a carbon precursor comprising nitrogen; obtaining or providing a substrate material; contacting the carbon precursor and the substrate material, to provide a sorbent starting material; and processing the sorbent starting material, to provide the unpromoted carbon sorbent comprising nitrogen.

Embodiment 53 provides the method of Embodiment 52, wherein obtaining or providing the carbon precursor comprising nitrogen comprises: obtaining or providing a carbonaceous material comprising carbon and a nitrogenous material comprising nitrogen; and contacting and heating the carbonaceous material and the nitrogenous material, to provide the carbon precursor comprising nitrogen.

Embodiment 54 provides a method of making an activated carbon sorbent, comprising: contacting a carbonaceous material and a nitrogenous material, to provide an unpromoted carbon sorbent comprising nitrogen; promoting at least a portion of the unpromoted sorbent by contacting the portion of the unpromoted sorbent with a promoter to form an activated carbon sorbent comprising activated carbon sorbent particles comprising nitrogen, wherein the concentration of nitrogen in the sorbent particles is higher than the concentration of nitrogen in the carbonaceous material.

Embodiment 55 provides an activated carbon sorbent made by the method of any one of Embodiments 51-54.

Embodiment 56 provides an activated carbon sorbent, comprising: a halogen- or halide-promoted activated carbon, the activated carbon comprising activated carbon sorbent particles comprising nitrogen in a surface layer of the sorbent particles.

Embodiment 57 provides the activated carbon sorbent of Embodiment 56, wherein the concentration of nitrogen in the surface layer of the sorbent particles is higher than the concentration of nitrogen in a core of the sorbent particles.

Embodiment 58 provides the activated carbon sorbent of any one of Embodiments 56-57, wherein the activated carbon sorbent particles have an average diameter of about 0.1 μm to about 1000 μm.

Embodiment 59 provides the activated carbon sorbent of any one of Embodiments 56-58, wherein the activated carbon is at least one of halogen-promoted, Group V halide-promoted, Group VI halide-promoted, hydrogen halide-promoted, ammonium halide-promoted, alkali earth metal halide-promoted, and alkaline earth metal halide-promoted.

Embodiment 60 provides the activated carbon sorbent of any one of Embodiments 56-59, wherein the activated carbon sorbent is inorganic matrix-supported, the inorganic matrix support comprising at least one of diatomaceous earth, a clay, a zeolite, or a mineral.

Embodiment 61 provides the activated carbon sorbent of any one of Embodiments 56-60, wherein the nitrogen is substantially homogenously distributed in the core of the activated carbon sorbent particles.

Embodiment 62 provides the activated carbon sorbent of any one of Embodiments 56-61, wherein the nitrogen in the surface layer of the particles at least partially decreases neutralization by HSO₃ ¹⁻ or SO₃ ²⁻ of carbocations in the activated carbon sorbent, as compared to a corresponding activated carbon sorbent comprising less or substantially no nitrogen in a corresponding particle surface layer under substantially similar conditions.

Embodiment 63 provides the activated carbon sorbent of any one of Embodiments 56-62, wherein the nitrogen in the surface layer of the particles at least partially blocks carbocations in the activated carbon from forming ionic bonds with HSO₃ ¹⁻ or SO₃ ²⁻, as compared to a corresponding activated carbon sorbent comprising less or substantially no nitrogen in a corresponding particle surface layer under substantially similar conditions.

Embodiment 64 provides the activated carbon sorbent of any one of Embodiments 56-63, wherein a first quantity of the activated carbon sorbent forms a mercury-sorbent composition at a first mercury adsorption rate in a gas composition comprising mercury wherein the concentration of sulfur(VI) in the gas composition is about 3-2000 ppm by mole, and wherein the first adsorption rate is higher than a mercury absorption rate of the first quantity of a corresponding activated carbon sorbent comprising at least one of a) less or substantially no nitrogen in a corresponding particle surface layer, b) less or substantially no halide- or halogen-promotion, and c) less or substantially no inorganic matrix support, wherein the activated carbon sorbent is inorganic-matrix supported.

Embodiment 65 provides the activated carbon sorbent of any one of Embodiments 56-64, wherein the nitrogen is derived from a nitrogen-containing organic or inorganic compound.

Embodiment 66 provides the activated carbon sorbent of any one of Embodiments 56-65, wherein the nitrogen is derived from indole, quinoxaline, carbazole, isoquinoline, nitrobenzene, urea, sulfamic acid, polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymer, vinylpyrrolidone-acrylic acid copolymer, vinylpyrrolidone-maleic acid copolymer, polyethylenimine, alanine, piperazine, quinolone, quinoxaline, diazabicyclooctane, an amino acid, an ammonium salt, or a combination thereof.

Embodiment 67 provides an activated carbon sorbent for use in mercury removal from a mercury-containing gas, the sorbent comprising: a halogen- or halide-promoted activated carbon comprising activated carbon particles, the particles comprising nitrogen in a surface layer, the nitrogen in the surface layer at sufficient concentration to at least one of a) decrease neutralization by HSO₃ ¹⁻ or SO₃ ²⁻ of carbocations in the activated carbon sorbent, as compared to a corresponding activated carbon sorbent comprising less or substantially no nitrogen in a corresponding particle surface layer under substantially similar conditions, and b) at least partially block carbocations in the activated carbon from forming ionic bonds with HSO₃ ¹⁻ or SO₃ ²⁻, as compared to a corresponding activated carbon sorbent comprising less or substantially no nitrogen in a corresponding particle surface layer under substantially similar conditions.

Embodiment 68 provides the apparatus or method of any one or any combination of Embodiments 1-67 optionally configured such that all elements or options recited are available to use or select from. 

What is claimed is:
 1. A method of removing mercury from a mercury-containing flue gas, the method comprising: combusting coal comprising an added promoter precursor that comprises NaBr, CaBr₂, NaCl, CaCl₂, KI, NaI, CaI₂, NH₄Br, NH₄Cl, NH₄F, NaF, Ca₂F, or a combination thereof, to form the mercury-containing flue gas comprising a halogen- or halide-promoter that comprises Cl⁻, HCl, Br⁻, HBr, I⁻, HI⁻, F⁻, HF, or a combination thereof; adding a nitrogen-containing compound and activated carbon sorbent particles together or separately into the mercury-containing flue gas upstream of a particle separation device, the nitrogen-containing compound comprising an ammonium salt, ammonia, urea, an inorganic nitrogen compound, or a combination thereof; capturing mercury from the mercury-containing gas with the activated carbon sorbent particles, wherein the activated carbon sorbent particles in the flue gas comprise nitrogen in a surface layer thereof, the concentration of nitrogen in the surface layer being higher than the concentration of nitrogen in a core of the sorbent particles, the core of the sorbent particles comprising nitrogen; and removing the activated carbon sorbent particles from the mercury-containing gas with the particle separation device.
 2. The method of claim 1, wherein the halogen- or halide-promoter comprises Br₂, Cl₂, I₂, F₂, ICl, or a combination thereof.
 3. The method of claim 1, wherein the promoter precursor comprises KI, NaI, CaI₂, or a combination thereof, and the promoter comprises I⁻, HI, or a combination thereof.
 4. The method of claim 1, wherein the promoter precursor comprises CaBr₂, and the promoter comprises Br⁻, HBr, or a combination thereof.
 5. The method of claim 1, wherein the promoter precursor comprises NaBr, and the promoter comprises Br⁻, HBr, or a combination thereof.
 6. The method of claim 1, wherein the nitrogen-containing compound comprises the ammonium salt, wherein the ammonium salt comprises an ammonium halide.
 7. The method of claim 1, wherein the nitrogen-containing compound comprises the ammonium salt, wherein the ammonium salt comprises ammonium chloride, ammonium bromide, or a combination thereof.
 8. The method of claim 1, wherein the nitrogen-containing compound comprises the ammonium salt, wherein the ammonium salt comprises ammonium sulfate.
 9. The method of claim 1, wherein the nitrogen-containing compound comprises the ammonium salt, wherein the ammonium salt comprises ammonium sulfate and the promoter precursor comprises NaBr, CaBr₂, or a combination thereof.
 10. The method of claim 1, wherein the nitrogen-containing compound comprises ammonia.
 11. The method of claim 1, wherein the nitrogen-containing compound comprises urea.
 12. The method of claim 1, wherein the nitrogen-containing compound comprises the inorganic nitrogen compound, wherein the inorganic nitrogen compound is at least one of nitric acid, nitrous acid, nitrogen dioxide, and nitrogen oxide.
 13. The method of claim 1, comprising promoting the activated carbon sorbent particles in the mercury-containing flue gas with the promoter.
 14. The method of claim 1, wherein the surface layer of the activated carbon sorbent particles comprises a layer at the surface of the particles having a thickness of about 0.001% to about 50% of the radius of the particles.
 15. The method of claim 1, wherein the surface layer of the activated carbon sorbent particles in the flue gas is about 0.001 wt % to about 99 wt % nitrogen.
 16. The method of claim 1, wherein the mercury-containing gas comprises a concentration of sulfur(VI) and the concentration of sulfur(VI) in the mercury-containing gas is greater than or equal to about 1 ppm by mole and the promoted activated carbon sorbent particles form a mercury-sorbent composition at a higher absorption rate relative to corresponding promoted activated carbon sorbent particles comprising at least one of a) less or substantially no nitrogen in a corresponding particle surface layer, b) less or substantially no halide- or halogen-promotion.
 17. The method of claim 1, wherein the activated carbon sorbent particles have an average diameter of about 0.1 micron to about 1,000 microns.
 18. A method of removing mercury from a mercury-containing flue gas, the method comprising: combusting coal comprising an added promoter precursor that comprises NaBr, to form the mercury-containing flue gas comprising a halogen- or halide-promoter that comprises Br, HBr, or a combination thereof; injecting ammonium sulfate and activated carbon sorbent particles together or separately into the mercury-containing flue gas upstream of a particle separation device; capturing mercury from the mercury-containing gas with the activated carbon sorbent particles, wherein the activated carbon sorbent particles in the flue gas comprise nitrogen in a surface layer thereof, the concentration of nitrogen in the surface layer being higher than the concentration of nitrogen in a core of the sorbent particles, the core of the sorbent particles comprising nitrogen; and removing the activated carbon sorbent particles from the mercury-containing gas with the particle separation device.
 19. A method of removing mercury from a mercury-containing flue gas, the method comprising: combusting coal comprising an added promoter precursor that comprises CaBr₂, to form the mercury-containing flue gas comprising a halogen- or halide-promoter that comprises Br⁻, HBr, or a combination thereof; injecting ammonium sulfate and activated carbon sorbent particles together or separately into the mercury-containing flue gas upstream of a particle separation device; capturing mercury from the mercury-containing gas with the activated carbon sorbent particles, wherein the activated carbon sorbent particles in the flue gas comprise nitrogen in a surface layer thereof, the concentration of nitrogen in the surface layer being higher than the concentration of nitrogen in a core of the sorbent particles, the core of the sorbent particles comprising nitrogen; and removing the activated carbon sorbent particles from the mercury-containing gas with the particle separation device. 